Electric arc lamp



July 8, 1941. J. ANDERSON 2,248,050

ELECTRIC ARC LAMP Filed Sept. 18, 1939 3 She ets-Sheet 1 INVENTOR.650mg: J. ANDEQJO/V y 1941. G. J. ANDERSON 2 8,050

ELECTRIC ARC LAMP INVENTOR.

650265 J. ANDEPcSOV M PIE-L11.-

ATTORNEY.

Patented July 8, 1941 UNITED STATES Warner Bros. Pictures,Inc., NewYork,

PATENT OFFICE ELECTRIC ARC LAMP George J. Anderson, Hollywood, Calif.,assignor to corporation of Delaware Application September 18, 1939,Serial No. 295,472

8 Claims.

This invention relates to electric arc apparatus u and has particularreference to electric arc lamps.

One object of the invention is to accurately control the feeding of theelectrodes of an arc lamp toward each other to compensate for theburning away of the tips thereof.

Another object is to maintain correct relative feeding movement of apair of electrodes toward each other and to enable such relative feedingmovement to be varied as desired, with or without varying the rotationof one of the electrodes.

Another object is to provide for selective, automatic, or manual feed ofan electrode for an electric arc apparatus.

Another object is to enable quick removal of N. Y., a

' ratus, as a unit, from its housing to facilitate rean electrodefeeding apparatus from its housing, 5

pair or replacement of that unit. This feature is also of considerableimportance in the motion picture industry where the loss of timeincurred due to repair or replacement of any equipment is very costly.

The manner in which the above and other objects of the invention areaccomplished will be readily apparent from the following specification,when read in conjunction with the accompanying drawings, wherein:

Fig. 1 is a longitudinal sectional view of an electric arc lamp andhousing therefor, embodying the present invention.

Fig. 2 is a transverse sectional View through the electric arc apparatusand housing therefor, and

to provide an unflickering beam of light. To pro- 1 duce thisunflickering illumination, one of the electrodes, generally thepositive, is caused to be rotated about its axis at a steady rate, whilebeing fed longitudinally, so as to uniformly burn,

or form a symmetrical crater, at the tip of that electrode.

The present invention contemplates a simplified drive assembly forrotating one of the electrodes, i. e., the positive, and for feeding theelectrodes at desired relative longitudinal speeds,

accommodate electrodes having different burning rates, and may also beregulated to compensate for varying current supply for the electrodeswhile being capable of feeding the same at such a speed as to maintain amaximum of brilliancy and uniformity of illumination. This latterfeature is of considerable importance in the motion picture industry,where, in the photographing of sets or scenes, large numbers of arclamps are usually employed. Many of these lamps are turned off and on atdifferent times, thus greatly changing the load conditions of thecurrent supply and consequently affecting a noticeable change in.voltage. This is particularly true in cases where port-dole generatingequipment of is taken along the line 22 of Fig. 1.

Fig. 3 is a sectional plan view of the rear panel and part of the arclamp housing and is taken along the lines 33 of Fig. 1.

Fig. 4 is a sectional plan View of the intermittent driving mechanismfor the negative electrode feeding head and is taken along the line 44of Fig. 2.

Fig. 5 is a transverse sectional View through the intermittent drive andis taken along the line 55 of Fig. 4.

Fig. 6 is a transverse sectional view through the feeding mechanism forthe negative electrode and is taken along the line 66 of Fig. 1.

Fig. 7 is a longitudinal sectional view through the positive electrodefeeding head and is taken substantially along the line of Fig. 2.

Fig. 8 is a transverse sectional view through the positive electrodefeeding head and is taken along the line 8--8 of Fig. 7.

Fig. 9 is a transverse sectional View through the feed gears and supporttherefor in the positive electrode feeding head, and is taken along theline 9-9 of Fig. 7,

Fig. 10 is a sectional view through the positive electrode headillustrating particularly the man ual feed drive therefor, and is takenalong line l0--l0 of Fig. 8.

Fig. 11 is a transverse sectional View through the combined contactbrush and heat shield unit for the positive electrode feeding head, andis taken along the line HH of Fig. '7.

Referring in particular to Fig. 1 and Fig. 2,

the electric arc lamp assembly comprises a boxshaped housing I5, open atthe top thereof and having 'bafiie plates l2 and I3 extending across thetop thereof to form a light seal while perinitting a draft of air to bepassed therethrough. Openings as at l5, l6 and I! are formed in thelower portion of the walls of the housing It) to permit air to be passedupwardly therethrough for cooling purposes. The front wall [8 of housingit has an opening therein surrounded by a substantially cylindricalflange ii) in which is secured a lens 29 of the Fresnel type. The rearwall 2i of the housing if] has a rectangular opening 22 therein,normally closed by a rear cover member, or panel 23, which is removablysecured to the wall 2| by screws 24.

The electrode feeding assembly comprises a positive electrode feedingdevice or head generally indicated at 25 for feeding a positiveelectrode or carbon A, and a negative electrode feeding device or headgenerally indicated at 26 for feeding a negative electrode or carbon B.Both heads 25 anad 25 are supported by a base 21, to the under surfaceof which is secured a drive motor 28 for the purpose of driving theelectrode feeding mechanism in each head.

The base 22' has a pair of spaced ears, as at 29 and extending fromopposite sides thereof. These ears, as at 29 and 39, have bearingsformed therein and are movable along a pair of spaced parallel rods 3|and 32 extending from the front wall i8 to the rear wall 2| of thehousin it.

One of the rods 3| is screw threaded at 33 and is journalled at thefront end thereof in a bearing 34 provided in the front housing wall IS.The rear end of rod 3| is journalled in a bearing provided in the panel23. A handle 36 is secured on the end of rod 3| extending throughbearing whereby to enable manual rotation of the rod 3!. The bearing 35and rear end of rod (ii are so formed as to prevent endwise movement ofrod 3| relative to panel 23.

As will be noted in Fig. 1, ear 30 on base 21 is screw-threaded andmounted on the threaded portion 33 of rod 3|, whereby to cause movementof the entire electrode feeding assembly toward and away from lens 26 onrotation of the handle 36. That is, rotation of the handle 36 will causemovement of the arc produced across the tips of the positive electrode Aand the negative electrode B into or out of the focus of the lens 20.

As shown in Fig. 3, the rod 32 is secured at 38 to the rear panel 23,and is slidably received at the front end thereof in a bearing (notshown) similar to that of 34 and mounted or formed on the front wall |8of the housing In.

The positive electrode feeding head 25 is mounted on a sub-base 39 whichis supported by posts 52 anad 52 from the main base 21. A layer 39' ofinsulating material, such as asbestos or the like, is interposed betweenthe head 25 and the base 39 to electrically insulate this head.

Describing in detail the positive head 25, reference is had to Figs. '7,8, 9, 10, and 11, inclusive. Head 25 comprises a cylindrical housing 40,having legs 4| (Figs. 1 and 2) at the bottom thereof, which are securedby bolts 42 to the subbase 39. Bolts 42 pass through suitable insulatingbushings (not shown). The housing has an apertured end wall 43 at theforward end thereof, and is open at the rear thereof, there being acylindrical shoulder 44 formed thereon and adapted to snugly receive amating cylindrical portion of a casing 45. Casing 45 is open at the endthereof adjacent housing 40 and is removably secured to this housing byscrews 46. Housing 43 and casing 45 form a substantially enclosedcompartment to house the electrode feeding mechanism.

A bearing counterbore 41 is formed at the rear of the casing 45 toreceive a ballbearing assemly 4%]. A cap 49, having a centrally locatedelectrode receiving aperture 50 therein, is secured to the end of casing45 by screws 5|, to retain he bearing assembly 48 in the counterbore 41and prevent longitudinal movement thereof.

An electrode carrier generally indicated at 53 is rotatably supported bythe bearing assembly 48. Carrier 53 comprises a tubular member 54,having a longitudinally extending bore therethrough, to loosely receivethe positive electrode A. A crown gear member 55 is slidably fitted overthe member 54, and abuts a shoulder 56 formed on member 54.

A lock nut 51 threaded on the rear end of the member 54 is provided tosecure the gear member 55 to the tubular member 54, and also to lock themember 54 in the bearing assembly 48, to prevent longitudinal movementthereof.

Referring in particular to Figs. 7 and 9, it will be noted that theforward portion of the tubular member 54 is formed into an enlarged head58 having a longitudinally extending slot 59 formed therein. A pair ofdiametrically opposed, transversely extending grooves, 60 and 6|, arecut into the head 58, to receive and guide a pair of stub shafts 52 and63 therein, respectively. A pair of feed gears, or wheels, 64 and 65 arejournalled on the stub shafts 62 and 63, respectively. Gears 64 and 65are located in and guided against longitudinal movement by the opposedsides of the groove 58. A pair of tension springs 68 and 66 are providedbetween the ends of the stop shafts 62 and 63, to resiliently urge theteeth of the gears 64 and 65 into driving engagement with the surface ofthe positive electrode A. A spiral or scroll gear member 61 isjournalled on a bearing portion formed on the tubular member 54,directly behind the head 58, and has a set of spiral gear teeth 68formed on one face thereof which mesh with the teeth of the grippergears 64 and 65. From the above it will be noted that relative rotationof the tubular member 54 and spiral gear member 61 will cause rotationof the gears 64 and 65 about their respective shafts, to impart alongitudinal feeding movement of the positive electrode A.

A set of spur gear teeth 69 are formed on a periphery of gear 67.

Referring in particular to Figs '7 and 8, a threelobed cam 10 is securedto the face of the crown gear member 55, intermediate gears 55 and 6! byscrews. one of which is shown at 7|. A cam follower l2 rides on thesurface of cam 10 and is reciprocal in a guide block 13 which extendsthrough an opening formed in the casing 45 and is secured to this casingby screws, as at 14. That is, cam follower I2 is slidable, in asubstantially vertical direction, in a bearing formed in block 73. Acompression spring is interposed between the cam follower 12 and theblock '73 to resiliently urge the follower 12 into engagement with thecam 70.

A portion of the cam follower 72 extends through the top of the guideblock 13 and has a stop screw 15 screw threaded therethrough. The bottomend of screw 18 has a conical point formed thereon and adapted to engageany one of the teeth 69 on gear 61, when the cam follower it rides upona flattened portion 18 of cam 18. From the above it will be noted thaton rotation of the tubular member 54, the positive electrode A will berotated and the cam follower l2 will be reciprocated three times perrevolution of the member 54. As the cam follower 12 moves downwardly,the conical point of screw 16 engages a tooth on the periphery of thespiral gear member 6?, thereby arresting rotation of this member, and,due to the relative rotation between the head '58 and the gear 61, willeffect rotation of the gears 64 and 65 to cause feeding movement of theelectrode A. In other words, a feeding movement will be imparted to theelectrode A three times per revolution of the electrode carrier 53.

In the event that it is desired to regulate the rate of feeding of theelectrode A independently of the rate of rotation thereof, a lock nut19, threaded on screw 16 and abutting the upwardly extending portion ofthe cam follower- 12, is loosened, allowing the screw to be raised orlowered, whereby the interval of time during which the conical point ofscrew 16 is engaged with one of the teeth 89 may be regulated, which ofcourse will regulate the amount of each feeding impulse. That is, if thescrew 16 is lowered, the conical point of this screw will engage a toothtil at an earlier moment on the downward travel of the cam follower l2and will be disengaged from that tooth at a later moment, thus holdingthe gear t3! in a fixed position for a longer period of time. Since eachfeeding impulse of the electrode is of considerable duration, but causesonly a very short length of travel, and, furthermore, since there are aplurality of impulses for each rotation of the electrode, it will benoted that the slight unevenness of longitudinal feeding travel will beinsufficient to cause a flicker or change in the illumination of thearc.

The above mentioned positive electrode feeding head is described andclaimed in my Patent No. 2,1731% granted September 19, 1939, forElectrode feeding device for electric arc apparatus. However, in thatpatent, a series of serrations are provided around the periphery of thegear $2, in lieu of the gear teeth 89.

teferring to Figs. 1, 8 and 10, the electrode A is adapted to bemanually fed in a longitudinal direction, independently of the motordrive for the .two electrode feeding heads and 26, by a shaft whichextends rearwardly from the casing iii through a hole formed in panel 23and terminates in a handle 8|. Shaft 80 is divided into two sectionswhich are connected together, and insulated from each other, by acoupling 82 of insulating material, such as bakelite. The inner end ofshaft is journalled in a bearing 83 formed in the casing 45. A pinion 84is secured to the inner end of the shaft 80 and is adapted to mesh withthe gear teeth 69 formed on the gear member 61, but is normally out ofengagement therewith. When it is desired to manually feed the electrodeA; as, for example, when inserting a new electrode or when moving theelectrode into a correct alignment with the negative electrode B; thehandle 8| is pressed inwardly against the action of a compression spring85, interposed between the casing and the coupling 82. This actioncauses the gear 84 to move into mesh with the gear teeth 69, and, onrotation of the handle 8|, the spiral gear 6'1 will be rotated relativeto the head 58, to impart a feeding motion to the feed gears $4 and 65.

Due to the fact that the shaft 89 extends a considerable distance behindthe panel 23, it will be noted that the handle ill will not interferewith the focusing adjustment of the electrode feeding assembly.

Included in the positive head 25 is a combination contact brush andshield assembly, generally indicated at 8?, which is situated in frontof the housing ii-l to shield the electrode feeding mechanism of thepositive head 25 from the intense heat of the are produced across theelectrodes A and B. This assembly comprises a member 88 secured, as byscrews as, to the sub-base 39 through the insulating layer 38. Note thatmember does not touch the housing 40, thereby permitting an insulatinglayer of air to extend therebetween. Member 88 has an electrodereceiving aperture extending centrally therethrough, through whichelectrode A passes. A shield unit is secured in front of member 88 andcomprises, in part, a metal plate 90, secured by screws Q! to the frontface of the member 88. An asbestos plate 32 and a metal plate 93separated from the plate 522 by the spacers 94 are secured to the plate93 by screws S5. A horizontally extending channel 955 is provided in thefront face of the member 88 and has a stationary contact shoe 9?,secured therein by a lock screw (Figs. 7 and 11). Screw 38 passesthrough an elongated slot as, formed in shoe 9?, whereby this shoe maybe moved into different positions and then locked. The inner end of theshoe 91 is concave to fit the surface of the electrode A. Also mountedin the channel 96 is a springpressed movable contact shoe Hi9, alsohaving its inner end concave to fit the surface of the electrode A.

Current is supplied to the movable contact shoe H19 by a flexibleconductor 10! which is secured in a terminal clip I92. Clip I02 issecured to the end of contact shoe If!!! by a bolt Hi3, the head ofwhich is engaged by a lever I84 pivoted at Hi5 to brackets I06 extendingfrom the member I98. The opposite end of lever it is engaged by acompression spring I01 (Fig. 2).

The negative electrode feeding head 26 comprises an electrode clamp Hi9secured to the negative electrode B and slidable along a pair of spacedguide rods H6 and HI (Fig. 6). Rods ilii and Hi are secured at theiropposite ends in brackets H2 and H3 extending from a continuation of thesub-base 33. A screw threaded shaft Hd extends parallel to the electrodeB, intermediate rods HQ and HI and is suitably journalled at oppositeends thereof, in bearings formed in the brackets H2 and H3. Shaft H4 isalso slidable lengthwise a limited amount in its bearings.

A tooth H5, mounted on a lever H8 (Fig. 6), is carried by the clamp I09and is normally in engagement with the threads of shaft I 14, therebyforming a travelling nut member. Lever H6 is pivoted at H? to adepending portion of the clamp Hi9 and is spring pressed in a clockwisedirection to cause the tooth H5 to engage the shaft H4 by a spring H8.By depressing the lever lit, the tooth H5 will be moved out ofengagement with the shaft H4, thereby enabling the clamp its to be movedalong the rods Hi) and Hi, enabling the adjustment of the electrode Btoward or away from the electrode A. A bevel gear IN is slidably keyedon the screw threaded shaft H4 at the upper end thereof and ismaintained in continual mesh with a mating bevel gear I2I fixed to theend of a negative drive shaft I22 The above mentioned description of thedetails of the clamp I59, as well as the provision for allowing thescrew H4 to be moved lengthwise for striking the arc, is not a subjectof the present application and it is therefore not believed necessary todescribe the same in further detail.

Shaft I22 is journalled in bearings I23 and I24 formed on the sub-base39. The end of shaft I22 extends through the hole in panel 23 andterminates in a handle I25, to enable manual feeding operation of theelectrode B independent of the motor drive therefor. Shaft I22 isdivided into two sections which are insulated from each other by acoupling I25 of Bakelite or other insulating material.

Referring in particular to Fig. 2, the motor 28 has a gear reductionunit (not shown) provided in a housing I21 formed at one end bell of themotor. This gear reduction unit is connected to and drives a main driveshaft I29, which is journalled at the upper end thereof (Fig. '7) in abearing I33 formed in the casing 45. A bevel pinion i3! is formed on theupper end of shaft I29 and meshes with the crown gear 55 to drive theelectrode feeding mechanism of the positive head. Shaft I29 is dividedinto two sections which are connected together and insulated from eachother by a coupling I30 of Bakelite or like material.

A worm I3I (Figs. 4 and 5) is secured to shaft 1'29 intermediate itsends and meshes with a worm gear I32 loosely journalled on a sleeve I33which is secured to the negative drive shaft I22.

Worm gear I32 is maintained in engagement with a flange I34 on thesleeve I33 by a compression spring I 35, these members, (the flange I34and gear I32), forming the coacting elements of a friction clutch, toenable a non-positive drive connection between the worm gear I32 andshaft I22 to be maintained. A look nut I 3'! is threaded on the end ofsleeve I33 to retain the spring I35 under compression and is adjustablealong the sleeve I33 to vary the friction between the gear I32 andsleeve I33.

A three-lobed cam I33 is secured, in a suitable manner, to the worm gearI32 and is engaged by a cam follower I 39 slidably mounted in a guideblock I49. Block I40 is suitably secured to, and extends through, anopening formed in a protective housing I4I which surrounds the worm I3!and gear I32 and protects the same from carbon dust and the like.Housing MI is secured through the base 21, as by screws I42.

Cam follower I39 is similar to that of I2, there being a compressionspring I43 interposed between this cam follower and a well, formed inthe guide block 133, to resiliently press the cam follower in engagementwith the cam I38. A stop screw I44 is threaded through the cam followerI39 and is adapted to be adjustably locked in different positions by alock nut I45 threaded thereon. The inner end of screw I44 is pointed andis adapted to engage any one of a plurality of serrations provided onthe periphery of a. member I Member I43 is interposed between the gearI32 and the compression spring I35 and is slidably keyed to the sleeveI33 by means of a pin I41. Thus, member I46 forms another element of theaforementioned friction clutch. From the above, it will be noted that onrotation of the worm gear I32 by the Worm I3I on the main drive shaftI29, the cam I38 will reciprocate the cam follower I39 and,consequently, the stop screw I44, which will intermittently engage theserrated member I46 to arrest the rotation of the negative drive shaftI22. Adjustment of the stop screw I44 will act to change the periodduring which the serrated member I46 and, consequently, the feeding ofthe negative electrode B is maintained in a manner similar to thatdescribed in connection with the stop screw I6.

By arranging the motor 28 to one sideof the vertical plane passingthrough the positive electrode A and the negative drive shaft I 22, andby inclining the main drive shaft 29, as indicated in Fig. 2, asimplified drive connection between the shaft I 29 and the negativefeeding mechanism of the head 26 is obtained. This results in a minimumnumber of gears and other rotating parts to effect quiet operation aswell as a simple and economically manufactured driving mechanism.

In order to automatically strike the arc between the electrodes A and B,an electro-magnet I49 is provided for this purpose. This electro-magnetI49 is connected in series with the circuit through the electrodes A andB, and is supported on a metallic L-shaped base I50 which is suspendedby means of brackets or posts I5I from the bottom of the base 27. Ametal armature I52 is pivoted at I53 to the base I50 and is held in theposition illustrated in Fig. 1, when no current is being passed to thearc lamp, by a tension spring I54, extending between the armature I52and the ear 29 of base 27. Armature I52 is pivotally connected to oneend of a link I55 which, in turn, is pivotally con nected to one end ofa bell crank lever I53. Lever I56 is pivoted at I5! to the lower end ofthe sub-base 39 and has the other end thereof extending through anaperture I 51' in sub-base I39, and formed into a yoke (not shown) whichengages a groove I58 formed in the threaded shaft II 4. Shaft II 4 isreciprocal longitudinally thereof by the bell crank I53 to move theclamp I09 and electrode B from the striking position illustrated in Fig.1 to an operating position (not shown). This type of strike mechanism,i. e., the slidable rod H4 and bell crank I55, is well known in the artand it is therefore not deemed necessary to describe same in furtherdetail.

Bearing in mind the above description of the are striking mechanism, andassuming that the electrodes have been correctly positioned so that theywill contact each other in striking position, it will be noted that whencurrent is first passed through the lamp circuit, contact will be madeacross the tips of the electrodes to complete this lamp circuit. Soonafter the establishment of the circuit across the electrodes theelectro-magnet I49 will become effective to actuate the arrnature I52.Thus, the negative electrode B will be drawn downwardly a predetermineddistance to separate the tip thereof a desired distance from the tip ofthe electrode A to produce the arc.

A rheostat indicated at I59 is suitably secured to the inner surface ofthe panel 23 and is connected in the circuit. of motor 28 to enable thespeed thereof to be regulated. A control knob I60, extending on theexterior panel 23, enables adjustment of rheostat I59.

The procedure which may be followed in regulating the electrode feedingmechanism is to maintain the motor 28 at a constant speed, whereby tomaintain the rotation of electrode A constant, and to adjust the stopscrews 18 and M4 to regulate the feeding movements of the electrodes Aand B respectively, as desired. However, regulation of the feedingmovements may be obtained by merely regulating the speed of the motor 28by the rheostat I59. Another alternative method of regulating thefeeding speeds of the electrodes is to back off, or entirely remove, thestop screw I44, so as to enable the same to be ineffective to arrest therotation of the negative drive shaft I22. In this case, the speed of themotor 28 may be regulated to obtain the cor rect feeding speed of thenegative electrode B, while adjusting the stop screw 16 to obtain thecorrect feeding speed of the positive electrode A.

When it is desired to remove the electrode feeding assembly, includingthe positive head 25 and negative head 25, from the housing 19, forreplacement or repair, flexible conductors I62, extending between asuitable socket on the bottom of the housing [0 and a terminal block I53on the base 2'l,are removed. The screws 24,securing the panel 23 to therear wall 2| of the housing ID, are then removed, enabling the panel 23to be moved rearwardly, carrying the rods 3! and 32, as well as theentire electrode feeding unit and motor 28, out of the housing Ill. Itwill be seen that the entire assembly is then completely detached fromhousing HI. Since the forward ends of the rods 3i and 32 are merelyfitted in bearings at the forward wall 18 of the housing ID, no furtherdisconnecting of any of the supporting members of the electrode feedingassembly is required.

Although the invention has been described in connection with, and isparticularly applicable to, a lens type housing, it is to be understoodthat with certain obvious modifications, the apparatus of the inventionmay be applied to a reflective type housing. For example, the opening 22and the panel 23 covered thereby may be extended upwardly and areflector may be secured to the panel 23.

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is.

I claim:

1. Electric arc apparatus comprising the combination of a positiveelectrode feeding device, a negative electrode feeding device, a driveshaft for driving one of said devices, means for rotating said shaft, ashaft for driving the other of said devices, a frictional clutchoperatively connecting said last mentioned shaft to said first mentionedshaft for driving said other device, and means actuated by said firstshaft for intermittently rendering said clutch inoperative to drive saidother shaft.

2. Electric arc apparatus according to claim 1, comprising adjustablemeans for controlling said last mentioned means to vary the periodduring which said clutch is rendered inoperative.

3. Electric arc apparatus comprising the combination of an electrodefeeding device, a drive shaft for said device, a drive member rotatablymounted on said shaft, a frictional drive connection between said memberand said shaft, means for rotating said member, and means actuated bysaid member for intermittently operating said frictional driveconnection for arresting the rotation of said drive shaft.

4. Electric arc apparatus comprising the combination of an electrodefeeding device, a drive shaft for said device, a member rotatablymounted on said shaft, a frictional drive connection between said memberand said shaft, a cam operatively connected to said member, a camfollower movable by said cam, a stop member operable by said camfollower and adapted to arrest the rotation of said shaft on movement ofsaid cam follower by said shaft, and means for rotating said member.

5. Electric are apparatus according to claim 4, comprising an adjustableconnection between said cam follower and said stop member whereby theperiod during which said shaft is arrested by said stop member may bevaried.

6. Electric arc apparatus comprising the combination of an electrodefeeding device, a drive shaft for said device. means on said shaftforming a clutch element, a drive member rotatably carried by said shaftand forming a second clutch element adapted to engage said firstmentioned clutch element to form a driving connection with said shaft, acam operatively connected to said drive member, a serrated memberslidably keyed to said shaft adjacent said drive member and on the sidethereof opposite said first mentioned clutch element, means forresiliently urging said serrated member against said drive member toeffect a drive connection between; said drive member and said shaft,means for rotating said drive member, and means actuated by said cam forperiodically arresting the rotation of said serrated member.

7. Electric arc apparatus comprising the combination of a positiveelectrode feeding head, a negative electrode feeding head, a drive shaftfor said positive head, means for rotating said drive shaft, a seconddrive shaft for said negative head, a gear operatively connected to saidfirst mentioned shaft, a second gear rotatably mounted on said secondshaft and meshing with said first mentioned gear, means forming africtional drive connection between said second gear and said secondshaft, and means comprising a cam on said second gear for periodicallyinterrupting the rotation of said second shaft.

8. Electric arc apparatus comprising the combination of a base, negativeand positive electrode feeding heads on said base, a motor on said base,a substantially horizontally extending drive shaft terminating at saidnegative head, the axes of said positive head and said motor extendinghorizontally substantially parallel to said negative drive shaft withthe axis of said positive head and the axis of said negative drive shaftin substantially the same vertical plane and with the axis of said motoroffset to one side of said plane, and a substantially straight shaftextending from said motor to said positive head at one side of saidnegative drive shaft and a worm on said substantially straight shaft anda cooperating worm wheel on said negative drive shaft.

GEORGE J. ANDERSON.

